Understanding the Menthol Dose in Cough Syrup
Cough syrup labels list menthol as an active ingredient with a per-dose amount, like 5 mg per 5 mL (1 teaspoon). For a 16 oz bottle, which holds about 473 mL, the total menthol depends on the number of doses and concentration.
Calculating Total Menthol Needed
Assume 5 mg menthol per 5 mL dose (standard for many OTC syrups like Robitussin or Delsym variants):
- Doses per bottle: 473 mL ÷ 5 mL = 94.6 doses (round to 94 full doses).
- Total menthol: 94 doses × 5 mg = 470 mg.
Round up to 500 mg for manufacturing overage (typically 5-10% extra to ensure label potency through shelf life).
Adjusting for Different Concentrations
| Per-Dose Menthol | Example Products | Total in 16 oz Bottle |
|------------------|------------------|-----------------------|
| 5 mg/5 mL | Robitussin CF | ~470 mg |
| 10 mg/5 mL | Some menthol-heavy formulas | ~940 mg |
| 2.5 mg/5 mL | Pediatric versions | ~235 mg |
Check the label's "Drug Facts" for exact mg per 5 mL. Menthol is ~0.1% w/v in most syrups (e.g., 5 mg/5 mL = 0.1%).
How Much to Buy or Add
- Pure menthol crystals: Buy 500-600 mg (0.5-0.6 g) for a 470 mg target. USP-grade crystals dissolve in syrup base at 1:1000 ratio.
- Menthol solution (10% in alcohol): Need ~5 mL for 500 mg.
- Scale by bottle size: For 8 oz (236 mL), halve to 235 mg.
Regulatory and Practical Notes
FDA requires exact active amounts on labels; home mixing risks under/over-dosing. Menthol provides cooling sensation, not cure—combine with dextromethorphan or guaifenesin if formulating full syrup. Source crystals from lab suppliers like Sigma-Aldrich; verify purity >99%. Test final concentration via HPLC if commercial.