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Drug Interactions with Foods and Beverages

If you take foods and beverages together with drugs, they may interact in such a way that affects the way the drugs work in our body. This is called food-drug interactions. Foods can affect the degree and rate at which a drug is being absorbed, broken down and excreted. This may not only prevent a drug from working effectively, but also predispose one to develop side effects.

There are a variety of foods/beverages that may have interaction with drugs. The followings are some examples.

1. Alcohol

If you are taking any sort of medication, it is recommended that you should avoid alcohol, which can increase or decrease the effect of many drugs.

2. Caffeine-containing food

Beverages such as coffee, tea, soft drinks and other energy drinks have caffeine. Caffeine can stimulate the central nervous system and increase blood pressure as well as attributing some diuretic effect as well. Caffeine is going to be broken down in the liver at the end. A number of drugs can interfere this mechanism in the liver and subsequently increase the caffeine level in blood; examples are ciprofloxacin, cimetidine and oral contraceptives. Ciprofloxacin is a prescription-only medicine. Oral dose forms of cimetidine are available over the counter; but the injectable form is a prescription-only medicine. Most oral contraceptives are available over the counter; but some oral contraceptives are on prescription-only.

On the other hand, caffeine also inhibits the metabolism of drugs such as theophylline resulting in increasing theophylline blood level, thus predisposing patients to its side effects including insomnia and cardiac arrhythmia. Theophylline is a medicine available for sale when it is sold under the supervision of a pharmacist.

3. Calcium-containing food

Calcium is good for growth and maintenance of strong teeth and bones. Dairy products such as milk, cheese, yogurt and ice cream, green leafy vegetables and tofu are rich in calcium. Nowadays, there are more and more calcium fortified fruit juices, breakfast cereals, soy products (e.g. soy milk) or dairy products (e.g. milk, cheese) on market. The calcium in the food may decrease the absorption of drugs. Typical examples are the antibiotics like tetracycline, ciprofloxacin, and levofloxacin; which may be less effective when taken at the same time with calcium rich food. And, drugs with low bioavailability such as bisphosphates (i.e. alendronate, risedronate, ibandronate) are especially problematic with these foods. These medications that interact with calcium are prescription-only medicines and should be taken according to doctor’s instruction. It is better to avoid concomitant intake with calcium-rich food or supplement, and it is advisable to separate their intake for at least 30 minutes.

Some drugs may increase the calcium level in the body, such as antacids (e.g. those with calcium carbonate), thiazide diuretics (hydrochlorothiazide, indapamide, metolazone), lithium and thyroxine. Antacids can be available over the counter; while thiazide diuretics, lithium and thyroxine are prescription-only medicines. Attention should be paid when food rich in calcium is taken with these drugs to avoid building up an excessive high calcium level in the body which may lead to nausea and vomiting, polyuria, constipation, abdominal pain and even seizure and coma.

4. Fruit Juice: Grapefruit Juice, Apple Juice, and Orange Juice

Grapefruit juice is one of the well-known juices that may interact with drugs. It inhibits an enzyme in the intestine that can reduce the metabolism of drugs and increase the risk of developing side effects. There are a wide range of drugs that may interact with grapefruit juice. Examples include cholesterol-lowering statins (and red yeast rice products), blood-pressure lowering drugs (calcium-channel blocker e.g. amlodipine, nifedipine and verapamil), estrogen containing oral contraceptives, tricyclic antidepressant (e.g. amitriptyline and clomipramine), a drug used for the prevention of organ transplant rejection (cyclosporine), and antimalarial drugs (e.g. quinine). The drugs above that interact with grapefruit juice are, in general, prescription-only medicines. Nevertheless, for oral contraceptives (as mentioned earlier), most of them are available over the counter; only some are on prescription-only. Statins are prescription-only medicines, including lovastatin when contained in pharmaceutical products.

Apple juice and orange juice are the other examples of fruit juice that may interact with drugs. They compete with drugs to be absorbed, resulting in lower level of drugs being absorbed into the blood stream. Absorption of fexofenadine (an antihistamine), is modestly reduced when taken with orange juice and apple juice. Other antihistamine like cetirizine and loratadine may be affected but not to the same extent as fexofenadine. Fexofenadine is available for sale under the supervision of a pharmacist; while cetirizine can on the other hand be available over the counter in open shelves. In general, the sale of loratadine needs to be supervised by a pharmacist. But when loratadine is contained in pharmaceutical products labelled for the relief of the symptoms of allergic rhinitis only, it can then be available in over the counter in open shelves.

5. Red Yeast Rice

Red Yeast Rice” (abbreviated: RYR) is obtained from fermenting rice with some specific fungi (such as those named Monascus purpureus). RYR is also known as red fermented rice, beni-koji, angkak, and hong qu (Chinese name: 紅麴米/紅麴/红曲/赤曲/丹曲). It should be distinguished from the “red rice”, which can mean the unmilled or semi-milled paddy (rough rice) with the “red bran”. While red rice can be a staple; the red yeast rice is NOT consumed as a staple.

Red Yeast Rice
(NOT a staple)
versus Red Rice
(a staple)

The RYR has the rice grain shape but is brittle; and is often broken into parts. It is purplish-red or brownish-red in colour; and the broken sections are usually pinkish. It can stain fingers, and has sour smell.

RYR has been used traditionally as food condiment, coloring, preservative, and also an ingredient in wine brewing. In the Chinese medicine, RYR was documented in literature as “strengthening the digestive function, beneficial to the vital energy, and giving warmth to the body core (健脾、益氣、溫中)” . Contemporary medicinal science has discovered that a substance “monacolin K” in RYR contributes to lowering blood cholesterol level.

In fact, monacolin K consists of two chemical forms: the acid form and the lactone form. The lactone form is chemically identical to a drug substance named “lovastatin” (Figure). Lovastatin, as a chemical drug, has been well-known for reducing cholesterol level. It belongs to a class of drugs called “statins”. In other words, RYR may contain a pharmacologically active substance lovastatin.

Conventional RYR-containing food or health supplement may contain variable amount of “lovastatin”. Anyone taking the products containing RYR should be cautious as they may experience drug effects similar to that of lovastatin; and it is possible that the RYR may interact with other medications.

The ingredient lovastatin itself can affect liver function. Pregnant woman or breastfeeding mother should not take pharmaceutical products containing lovastatin. In fact, RYR products (containing lovastatin) have the potential for its effect on liver. Patients with the liver disease, and pregnant woman or breastfeeding mother shall be cautious when consuming RYR products.

Lovastatin itself may interact with other drugs, RYR containing products would also have the potential to affect other medications and vice versa. For example, lovastatin containing pharmaceutical products should not be taken with drugs (e.g. itraconazole, ketoconazole, erythromycin, gemfibrozil) that may inhibit the liver enzymes. If taken together, there would be higher risk of developing muscle inflammation, and other side effects.

If you take the RYR products with other medicines containing lovastatin or other cholesterol lowering agent, there could be a variable degree of additive effect on the cholesterol lowering action. It is necessary to tell your doctor if you are on the RYR products, so that he will be able to give you appropriate advice.

Under the Pharmacy and Poisons Ordinance, statins including "lovastatin when contained in pharmaceutical products” are prescription-only medicines.

6. Potassium-containing foods

Some food such as beans and peas, nuts, fruits (e.g. banana, oranges, avocados), green leafy vegetables, white beans and salt substitute are rich in potassium. Potassium is an essential nutrient used to maintain fluid and electrolyte balance in the body. However, imbalance of potassium level in the body will be harmful which can lead to nausea, vomiting and even cardiac arrest. There are several prescription drugs that increase amount of potassium in the body; for example, angiotensin converting enzyme inhibitors (ACEIs) used in hyperstension (i.e. captopril, lisinopril, ramipril), digoxin for the treatment of heart failure, and triamterene a potassium-sparing diuretic. Intake large amounts of foods, fruit juice and vegetable soup that are high in potassium content should be avoided when taking these drugs.

7. Tyramine-containing food

Tyramine is naturally found in protein-containing foods. The level of tyramine is increased with respect to the food aging. High level of tyramine can cause a sudden, dangerous increase in blood pressure. Normally any ingested tyramine is rapidly broken down in our intestine and liver. However, as the enzyme activity is inhibited, there could be a rapid rise in blood pressure as a result. Several prescription drugs could interfere with the metabolism of tyramine, such as Monoamine Oxidase Inhibitors (MAOIs) which include moclobemide (an antidepressant), linezolid (an antibacterial agent) and isoniazid (an anti-tuberculosis agent).

Fermented foods, smoked foods and foods that are spoiled or not stored properly may contain tyramine. Avoid large amount of foods and drinks high in tyramine while taking these drugs. Please refer to Table.1 for foods and beverages containing high level of tyramine.

Beef or chicken liver, dried sausage
Avocados, banana, dried fruits e.g. raisins and prunes
Red wine
Aged and mature cheeses, such as aged cheddar and Swiss; blue cheeses such as Stilton and Gorgonzola; and Camembert. Cheeses made from pasteurized milk are less likely to contain high levels of tyramine, including American cheese, cottage cheese, ricotta, farm cheese and cream cheese.
Cured meats, which are meats treated with salt and nitrate or nitrite, such as dry-type summer sausages, pepperoni and salami.
Fermented cabbage, such as sauerkraut and kimchee.
Fermented soy products including soy sauce, teriyaki, soybean paste, fermented bean curd (fermented tofu), miso soup, tamari, natto, shoyu, and tempeh.
Fermented seafood products, such as fish sauce and shrimp sauce.
Yeast-extract spreads, such as Marmite, Vegemite.
Improperly stored foods or spoiled foods.
Broad bean pods, such as fava beans.
Alcoholic beverages. In particular, unpasteurized beers, including beers from microbreweries or on tap, are known to contain tyramine.
Table 1 : Foods and beverages containing high level of tyramine.

Health tips

  1. Whenever taking drugs, read the label and insert carefully, in particular check out for the warnings.

  2. Consult your family doctors or pharmacists if you have any concern on your food or beverages interaction with your drug.

Drug Office
Department of Health
Feb 2020