Contraceptive pills

It has been hypothesized that interference of some antibiotics with the efficiency of birth control pills is thought to occur in two ways. Modification of the intestinal flora may result in reduced absorption of estrogens. Second, induction of hepatic liver enzymes causing them to metabolize the pill's active ingredients faster may affect the pill's usefulness. However, the majority of studies indicate that antibiotics do not interfere with contraception. Even though a small percentage of women may experience decreased effectiveness of birth control pills while taking an antibiotic, the failure rate is comparable to the failure rate of those taking the pill. Moreover, there have been no studies that have conclusively demonstrated that disruption of the gut flora affects contraception. Interaction with the combined oral contraceptive pill through induction of hepatic enzymes by the broad-spectrum antibiotic rifampicin has been shown to occur. It is recommended that extra contraceptive measures are applied during antimicrobial therapy using these antimicrobials.
 

 Alcohol

Interactions between alcohol and antibiotics vary depending on the specific antibiotic, and, in some cases, can cause severe side-effects and decreased effectiveness.

"It is sensible to avoid drinking alcohol when taking medication. However, it is unlikely that drinking alcohol in moderation will cause problems if you are taking most "common" antibiotics." However, there are specific types of antibiotics with which alcohol should be avoided completely, because of serious side-effects.

Because of the risks of side-effects and effectiveness, one should check the specific indications on the specific antibiotic, but there is no categorical danger in mixing alcohol and [some] antibiotics. Despite the lack of a categorical counterindication, the belief that alcohol and antibiotics should never be mixed is widespread, as indicated in a survey in one British clinic.

"[P]atients often assume that they should avoid alcohol when taking any antibiotics. ...this belief has no foundation."

One potential source of the myth is from STD clinics in the 1950s and 1960s.Doctors gave the advice for moral reasons as they were worried that alcohol would reduce the inhibitions of sufferers and lead to further spread of diseases such as gonorrhoea. It has been suggested, but not corroborated, that the origin of this myth centers on the fact that, during World War II, penicillin was in short supply and was recycled from urine; convalescing soldiers that drank beer produced a greater volume of urine, and, thus, were banned from drinking beer, leading to the belief that alcohol interacted poorly with antibiotics.

 Specific effects

By way of side-effects, certain antibiotics, including metronidazole, tinidazole, cephamandole, latamoxef, cefoperazone, cefmenoxime, and furazolidone, cause a disulfiram-like chemical reaction with alcohol by inhibiting metabolism by acetaldehyde dehydrogenase, leading to serious side-effects, which include severe vomiting, nausea, and shortness of breath. Alcohol consumption while taking such antibiotics is, therefore, prohibited.

Other effects of alcohol involve the activity of liver enzymes, which break down the antibiotics. In addition, serum levels of doxycycline and erythromycin succinate^{[clarification needed]} may, in certain circumstances, be significantly reduced by alcohol consumption. This is particularly important, since these drugs are bacteriostatic and require a sustained level of the drug in the body to be effective: Increased metabolism and clearance would result in diminished pharmacotherapeutic effect.

Alcohol can interfere with the activity or metabolization of antibiotics