Alpha GPC (Alpha-glycerophosphocholine) doses as high as 1000 mg three times daily have been used in some studies, but other studies report significant effects in volunteers at dosages as low as 600 mg once daily, at least in terms of boosting growth hormone (GH) . As a nootropic, the general recommended dosage is 100-500 mg one to two times daily and it can be consumed before or after a meal.
Side effects of excessive intake include:
- a fishy body odor
- brain fog
- gastrointestinal (GI) distress
Rodent lethal dose (LD-50) is in the order of 10,000 mg/kg. Even though Alpha GPC is a natural substance occurring in the body, using doses at these excessive ranges certainly has the capability to be toxic in humans.
Stacking with ALCAR Benefits
One study reported Alpha GPC in conjunction with acetyl-L-carnitine (ALCAR) and phosphatidylserine (PS), as co-factors, enhanced the expression of enzymes relevant to docosahexaenoic acid (DHA) synthesis.
Alpha GPC, ALCAR, and PS all occur naturally in the brains of humans and other mammals therefore, they are not synthetic chemicals. Stacking GPC + ALCAR + PS may have a range of beneficial effects but may also exuberate the risk of side effects. Alpha-GPC is especially useful in people whose diet is deficient in choline.
Alpha GPC 99% vs. 50%
The difference between the 99% and 50% versions is the amount of active substance and byproduct left over during production. The byproducts of chemical synthesis, which include phospholipid intermediates and unreacted lecithin, are thought to be harmless and carry less nootropic benefit than GPC itself. The 99% version has more GPC and less by-product left over during production therefore, it is more expensive than its 50% alternative. Encapsulated Alpha GPC is almost always manufactured from the 50% version due to the difficulty involved in encapsulating the 99% version. This is because the 99% version is very hygroscopic and will turn oily after prolonged time at ambient temperature and humidity.
The synthesis of Alpha-GPC  and phosphatidylserine  are some of the more difficult ones, and represent a challenge to chemists. New and improved methods of synthesis are always being discovered, and this is expected to eventually drive the price down. Despite its high price today relative to other forms of choline, GPC is the most efficient, bioavailable , blood-brain-barrier permeable source of choline, and is a very sensible choice to try for those who may be suffering from a choline deficiency [4a]. Although with such a potent source, one should realize a rebound may easily occur, landing oneself in an excess [4b].
Naturally Occurring Alpha GPC
Although PS is abundant in common foods, Alpha GPC is present in very limited amounts in common foods, and ALCAR is practically nonexistent in dietary form, except in trace amounts (meat sources contain mostly l-carnitine, the unacetylated version, which does not permeate the BBB, and is not as useful for brain health). ALCAR is known to increase markers of oxidative stress above 12g, while doses of 1200 mg and 4g were shown to reduce markers.
Alpha GPC is present naturally in highest amounts within organ meats, typically the brain and heart, which is a repeating theme in these naturally-occurring animal-based nootropic supplements. GPC is also notable in smaller amounts within dairy products and wheat germ.
Benefits of Alpha GPC
The benefits of GPC on the elderly are too numerous to be confined to a brief essay [5a], and consideration will therefore be limited to effects in healthy and young subjects.
Alpha GPC is known to act synergistically with piracetam, acetyl-L-carnitine (ALCAR), phosphatidylserine (PS), and phosphatidylcholine. In terms of boosting function in healthy young patients, it outperforms aniracetam in one study [5b]. It was shown to contribute to increased alertness, focus and reduced reaction time, although some habituation or tolerance occurred after four weeks [6a]. Therefore, this compound may be best cycled, especially if the user feels it has become less effective than it once was.
Unsurprisingly, it reverses deficits induced by muscarinic nicotinic acetylcholine antagonists. It also contributes to enhanced hippocampal cholinergic transmission and long-term potentiation (LTP), again alongside ALCAR + PS [6b].