Since they derive from a strong acid but weak base, they are both at about pH = 5; as a consequence, the morphine salts are mixed with small amounts of NaOH to make them suitable for injection.A number of salts of morphine are used, with the most common in current clinical use being the hydrochloride, sulfate, tartrate, and citrate; less commonly methobromide, hydrobromide, hydroiodide, lactate, chloride, and bitartrate and the others listed below. Morphine diacetate (heroin) is not a salt, but rather a further derivative, see above.Morphine meconate is a major form of the alkaloid in the poppy, as is morphine pectinate, nitrate, sulfate, and some others. Like codeine, dihydrocodeine and other (especially older) opiates, morphine has been used as the salicylate salt by some suppliers and can be easily compounded, imparting the therapeutic advantage of both the opioid and the NSAID; multiple barbiturate salts of morphine were also used in the past, as was/is morphine valerate, the salt of the acid being the active principle of valerian. Calcium morphenate is the intermediate in various latex and poppy-straw methods of morphine production, more rarely sodium morphenate takes its place. Morphine ascorbate and other salts such as the tannate, citrate, and acetate, phosphate, valerate and others may be present in poppy tea depending on the method of preparation.The salts listed by the United States Drug Enforcement Administration for reporting purposes, in addition to a few others, are as follows:

Production
In the opium poppy, the alkaloids are bound to meconic acid.
Occurrence of morphine in other Papaverales and Papaveraceae, as well as in some species of hops and mulberry trees has not been confirmed. Morphine is produced most predominantly early in the life cycle of the plant. Past the optimum point for extraction, various processes in the plant produce codeine, thebaine, and in some cases negligible amounts of hydromorphone, dihydromorphine, dihydrocodeine, tetrahydro-thebaine, and hydrocodone (these compounds are rather synthesized from thebaine and oripavine). In the brain of mammals, morphine is detectable in trace steady-state concentrations. The human body also produces endorphins, which are chemically related endogenous opioid peptides that function as neuropeptides and have similar effects to morphine. Human biosynthesis
Morphine is an endogenous opioid in humans that can be synthesized by and released from various human cells, including white blood cells. CYP2D6, a cytochrome P450 isoenzyme, catalyzes the biosynthesis of morphine from codeine and dopamine from tyramine along the biosynthetic pathway of morphine in humans. The morphine biosynthetic pathway in humans occurs as follows:L-tyrosine → para-tyramine or L-DOPA → dopamine → (S)-norlaudanosoline → (S)-reticuline → 1,2-dehydroretinulinium → (R)-reticuline → salutaridine → salutaridinol → thebaine → neopinone → codeinone → codeine → morphine (S)-Norlaudanosoline (also known as tetrahydropapaveroline) can also be synthesized from 3,4-dihydroxyphenylacetaldehyde (DOPAL), a metabolite of L-DOPA and dopamine. Urinary concentrations of endogenous codeine and morphine have been found to significantly increase in individuals taking L-DOPA for the treatment of Parkinsons disease. Biosynthesis in the opium poppy
Morphine is biosynthesized in the opium poppy from the tetrahydroisoquinoline reticuline. It is converted into salutaridine, thebaine, and oripavine.