2 More content was added, including examples and links. edited Aug 4 '15 at 7:16 pH13 - Yet another Philipp 6,68411 gold badge3030 silver badges6262 bronze badges Many drugs are not very soluble in water what is a common property for a lot of organic substances, including Codeine. Therefor it is very common to turn them into their hydrochlorid which is simply $$\text{Drug}\ce{.HCl}$$. [4] E.g., Crystal Meth got it's name from the crystals that the hydrochloride forms. And with this in mind I don't think that$$\hskip1.7in$$ Source: Wikimedia Commons Other examples are, e.g., Cocaine, Cetirizine, hydroxyzine, and many more. As your substance is either the hydrochloride or would turn into the hydrochloride in stomach acid hindersthere should not be any destructive influence on the absorptionstructure of the drugs butdrug. In fact it should even promote itpromotes the absorption. Without profound knowledge in medicinal chemistry or further knowledge in biochemistry I would also guess that this isOn the reason whyother hand, the better solubility of the corresponding hydrochloride is a relatively big problem for those drugs that should not get absorbed in the stomach but in. They need to be coated to "survive" the stomach acidity to reach the intestine are coated with acid resistable substanceswhere they should get absorbed. Many drugs are not very soluble in water. Therefor it is very common to turn them into their hydrochlorid which is simply $$\text{Drug}\ce{.HCl}$$. And with this in mind I don't think that the stomach acid hinders the absorption of the drugs but it should even promote it. Without profound knowledge in medicinal chemistry or further knowledge in biochemistry I would also guess that this is the reason why the drugs that should not get absorbed in the stomach but in the intestine are coated with acid resistable substances. Many drugs are not very soluble in water what is a common property for a lot of organic substances, including Codeine. Therefor it is very common to turn them into their hydrochlorid which is simply $$\text{Drug}\ce{.HCl}$$. [4] E.g., Crystal Meth got it's name from the crystals that the hydrochloride forms. $$\hskip1.7in$$ Source: Wikimedia Commons Other examples are, e.g., Cocaine, Cetirizine, hydroxyzine, and many more. As your substance is either the hydrochloride or would turn into the hydrochloride in stomach there should not be any destructive influence on the structure of the drug. In fact it even promotes the absorption. On the other hand, the better solubility of the corresponding hydrochloride is a relatively big problem for those drugs that should not get absorbed in the stomach. They need to be coated to "survive" the stomach acidity to reach the intestine where they should get absorbed. 1 answered Aug 3 '15 at 19:32 pH13 - Yet another Philipp 6,68411 gold badge3030 silver badges6262 bronze badges Many drugs are not very soluble in water. Therefor it is very common to turn them into their hydrochlorid which is simply $$\text{Drug}\ce{.HCl}$$. And with this in mind I don't think that the stomach acid hinders the absorption of the drugs but it should even promote it. Without profound knowledge in medicinal chemistry or further knowledge in biochemistry I would also guess that this is the reason why the drugs that should not get absorbed in the stomach but in the intestine are coated with acid resistable substances.