The Interaction of Certain Foods and Medicine

Grapefruit juice is known to strongly interact with some medicines. It does not reduce their effectiveness, but it increases the frequency and severity of adverse reactions. Two classes of drugs are particularly known for these interactions,these are some medicines used to lower cholesterol in the blood: simvastatin, and to a lesser extent, atovastatine. Grapefruit juice taken at the same time as simvastatin can multiply by 15 times the absorption of the drug and cause serious muscle damage. Immunosuppressants recommended against the rejection after an organ transplant, like tacrolimus and cyclosporine if taken with grapefruit juice on a regular basis can damage the kidneys.
The Afssaps advised to avoid taking grapefruit juice within two hours before taking these medicines, and limit consumption to less than a quarter of a liter per day. However, apple juice and orange juice are not known to cause interactions.

Caffeine
Avoid consuming caffeine during treatment with certain antibiotics such as enoxacin, ciprofloxacin and norfloxacin, used mainly to treat urinary tract infections (cystitis), and theophylline, an anti-asthmatic who has the same effects as caffeine.
These antibiotics hamper the elimination of caffeine and can therefore lead to an overdose of caffeine, or an addition of side-effects for theophylline. Too much caffeine leads to excitement, palpitations, tremors, sweating or hallucinations.
It is advisable to avoid drinking coffee, tea or soda containing caffeine for the duration of the antibiotic treatment or when using theophylline to reduce an asthma attack

Foods rich in vitamin K
Cabbage, brussels sprouts, broccoli, spinach, avocados, parsley, lettuce and offal are to be consumed sparingly with oral anticoagulants, used for thinning the blood. These foods are causing a decline in the effectiveness of treatment and therefore an increased risk of thrombosis (formation of clots in the veins).
It is advisable, if you are on treatment with oral anticoagulants, not to eat more than one serving of vegetables per day, and you should not suddenly change your eating habits, ceasing or increasing consumption.

Alcohol
Alcohol should be avoided with all drugs as it reduces alertness. Tranquilizers (anxiolytics like benzodiazepines), analgesics or antitussives based on codeine or tramadol, neuroleptics, some antidepressants, and some antiallergic drugs are very much known to cause these side effects if taken with alcohol.Taken together with these drugs, alcohol can cause drowsiness and reduce reflexes. These effects can have dramatic consequences, especially when driving or operating machinery.
Moreover, consumption of alcohol with anti-inflammatories (ibuprofen type), paracetamol or aspirin can cause heartburn or acid reflux because it acts on the liver enzymes and therefore increases the toxicity of these drugs.

Sources:
http://www.holisticonline.com/Herbal-Med/hol_herb_med_reac.htm