4-HO-pyr-T, or 4-hydroxy-N,N-tetramethylenetryptamine, is a lesser-known psychedelic drug. It is the 4-hydroxylanalog of pyr-T. 4-HO-pyr-T was first synthesized by Alexander Shulgin. In his book TiHKAL (Tryptamines I Have Known and Loved), neither the dosage nor the duration are known. 4-HO-pyr-T produces few to no effects. Very little data exists about the pharmacological properties, metabolism, and toxicity of 4-HO-pyr-T.