HB 1636 amends the Texas Controlled Substances Act to classify mifepristone and misoprostol as Schedule IV controlled substances, alongside carisoprodol, which is already listed. Mifepristone and misoprostol are medications commonly used together for medical abortions. Mifepristone blocks the hormone progesterone, necessary for pregnancy maintenance, while misoprostol induces contractions to expel the pregnancy. By designating these drugs as Schedule IV, the bill imposes stricter controls on their manufacture, distribution, and prescription, limiting their accessibility and usage. The changes apply only to offenses committed on or after the Act's effective date, with prior offenses governed by existing law.