What's actually in pre-workout supplements besides caffeine
Pre-made pre-workout supplements are marketed as an all-in-one solution for energy and focus, but the formula is usually a blend of several active ingredients, each working differently. Besides caffeine (usually the main component), a typical formula includes beta-alanine (reduces muscular fatigue, causes a characteristic skin tingle), citrulline malate (dilates blood vessels, improving blood flow and 'the pump'), taurine (involved in cellular fluid regulation), and sometimes additional stimulants beyond caffeine.
The problem with pre-made blends is that individual ingredient doses often aren't fully disclosed (hidden behind a 'proprietary blend'), and may fall short of the doses shown to be effective for each compound individually in clinical studies. Also, total stimulant load in some products is quite high and can cause side effects — anxiety, a racing heart, sleep problems — especially when stacked with coffee or energy drinks later the same day.
A reasonable alternative for anyone who wants to control exactly what they're taking: assemble the individual components separately (caffeine, and creatine or beta-alanine if desired) at known, well-studied doses, rather than relying on an opaque pre-made mix.