USMLE Step 1 Pharmacology & Biochemistry Guide [2026]

Pharmacology and Biochemistry account for over 30% of questions on the USMLE Step 1 (USMLE Specifications, 2026). Because these subjects heavily test mechanisms, pathways, and drug interactions, mastering high-yield cheat sheet concepts yields rapid performance gains.

This study guide summarizes essential Pharmacology and Biochemistry concepts tested on official NBME examinations.

Key Takeaways

• Pharmacology questions focus on mechanisms of action, major adverse effects, and cytochrome P450 enzyme inducers/inhibitors (USMLE Specifications, 2026).
• Biochemistry questions concentrate on rate-limiting enzymes, vitamin deficiency syndromes, and metabolic storage disorders.
• Memorizing autonomic nervous system receptor responses ( alpha-1, alpha-2, beta-1, beta-2, M_1, M3 ) is mandatory for answering cardiovascular and respiratory pharmacology items.

What Are High Yield Pharmacology Concepts on Step 1?

1. Cytochrome P450 Enzymes (Inducers vs Inhibitors)

• Common P450 Inducers (Decrease drug efficacy): Phenytoin, Carbamazepine, Rifampin, St. John's Wort, Chronic alcohol, Griseofulvin ("Modafinil & Chronic Alcohol Induce P450").
• Common P450 Inhibitors (Increase drug toxicity): Macrolides (Erythromycin), Azole antifungals, Cimetidine, Grapefruit juice, Protease inhibitors, Amiodarone.

2. Autonomic Nervous System Receptors

• ** alpha-1 **: Vascular smooth muscle constriction (IP3/DAG pathway).
• ** alpha-2 **: Sympathetic outflow decrease (Gi pathway, decreases cAMP).
• ** beta-1 **: Heart rate and contractility increase, renin release (Gs pathway, increases cAMP).
• ** beta-2 **: Bronchodilation, vasodilation (Gs pathway, increases cAMP).

3. Autonomic & Cardiovascular Pharmacology

• Antiarrhythmics (Classes I–IV): Class I (Na+ channel blockers), Class II (beta-blockers), Class III (K+ channel blockers like Amiodarone), Class IV (Ca2+ channel blockers like Verapamil/Diltiazem).
• Antihypertensives in Pregnancy: Hydralazine, Methyldopa, Labetalol, Nifedipine ("He Likes My Neonate").

For broader organ system integration, refer to our USMLE Step 1 High Yield Topics Guide.

What Are High Yield Biochemistry & Metabolic Pathways?

1. Rate-Limiting Enzymes in Metabolism

• Glycolysis: Phosphofructokinase-1 (PFK-1).
• Gluconeogenesis: Fructose-1,6-bisphosphatase.
• TCA Cycle: Isocitrate dehydrogenase.
• Glycogenesis: Glycogen synthase.
• Glycogenolysis: Glycogen phosphorylase.
• De Novo Purine Synthesis: PRPP amidotransferase.

2. Glycogen Storage Diseases (GSD)

• Von Gierke Disease (Type I): Glucose-6-phosphatase deficiency. Severe hypoglycemia, hepatomegaly, elevated blood lactate and uric acid.
• Pompe Disease (Type II): Lysosomal alpha-1,4-glucosidase deficiency. Cardiomegaly, hypertrophic cardiomyopathy, exercise intolerance ("Pompe affects the Pump").
• Cori Disease (Type III): Debranching enzyme deficiency. Milder hypoglycemia, normal blood lactate.
• McArdle Disease (Type V): Skeletal muscle glycogen phosphorylase deficiency. Muscle cramps, myoglobinuria with exercise.

To see how exam content specifications apply overall, check out our master Complete USMLE Step 1 Guide.

What Are High Yield Vitamin Deficiency Syndromes?

• Vitamin B1 (Thiamine): Wernicke-Korsakoff syndrome, Beriberi (Dry vs Wet with high-output heart failure).
• Vitamin B3 (Niacin): Pellagra (Diarrhea, Dementia, Dermatitis, Death).
• Vitamin B12 (Cobalamin): Subacute combined degeneration of spinal cord, megaloblastic anemia, elevated methylmalonic acid (MMA).

How to Memorize Pharmacology & Biochemistry Efficiently?

To practice pharmacology and biochemistry clinical vignettes, visit our USMLE Step 1 Practice Questions Guide.

To integrate these concepts into a complete study schedule, see our USMLE Step 1 Study Plan and test your retention with leading question banks reviewed in our Best USMLE Step 1 Qbanks Comparison.

Biochemistry questions on Step 1 almost never ask for pure enzyme structure. They present a patient with physical findings (e.g., infant with hypoglycemia and hepatomegaly) and ask which enzyme is deficient or which metabolite is accumulated upstream.