Importing controlled substances like Valium into the United States is strictly regulated:

It is generally a felony for an individual to import controlled substances via mail into the United States without being a DEA-registered importer. Critical Safety Risks

There have been reports of patients receiving Haloperidol (an antipsychotic) instead of Diazepam, leading to severe muscle contractions and other medical emergencies.

If you choose to use a Mexican pharmacy, prioritize those that are regulated: Medication from Mexico: How San Diegans cross to save money

The U.S. Food and Drug Administration (FDA) and State Department have issued multiple alerts regarding medications purchased from Mexico:

Medications may be expired, stored improperly, or have inconsistent potency compared to FDA-approved standards. How to Verify Pharmacy Legitimacy