• a tricyclic antidepressant (TCA) (used to treat depression, pain, or obsessive-compulsive disorder) such as amitriptyline (Elavil, Endep), doxepin (Sinequan), or clomipramine (Anafranil);
• other commonly used tricyclic antidepressants, including amoxapine (Asendin), desipramine (Norpramin), imipramine (Tofranil), nortriptyline (Pamelor), and protriptyline (Vivactil);
• a phenothiazine (used to treat mania, schizophrenia, other psychiatric conditions, and nausea and vomiting) such as chlorpromazine (Thorazine), fluphenazine (Prolixin), perphenazine (Trilafon), mesoridazine (Serentil), thioridazine (Mellaril), promazine (Sparine), trifluoperazine (Stelazine), and others;
• an antihistamine such as diphenhydramine (Benadryl, others), chlorpheniramine (Chlor-Trimeton, others), triprolidine (Actifed, others), brompheniramine (Dimetapp, others), clemastine (Tavist) and others (antihistamines are often found in prescription and over-the-counter cold, allergy, and sleep medicines);
• quinidine (Quinora, Quinaglute, Quinidex, Cardioquin);
• amantadine (Symmetrel);
• digoxin (Lanoxin, Lanoxicaps); or
• haloperidol (Haldol).

Drugs other than those listed here may also interact with biperiden. Therefore patients must first inform their doctor or pharmacist before taking any prescription or over-the-counter medicines, including herbal products.