Periactin is a medication containing 4 mg of Cyproheptadine HCl per tablet. This prescription medication comes in a package of 20 tablets manufactured by Algorithm. Each tablet contains 4 mg of Cyproheptadine HCl as the active ingredient. The medication is packaged in tablet form for oral administration. As this is a prescription medication, it should only be taken under the direction and supervision of a healthcare provider.