These covariates included HDL (high-density lipoprotein) cholesterol, LDL (low-density lipoprotein) cholesterol, HDL cholesterol ratio, triglycerides, sitting diastolic and systolic blood pressure (mean of three measures), history of high blood pressure, history of stroke or cardiovascular disease, Fazekas score, FEV1, alcohol units per week, hemoglobin A1c, diagnosis of diabetes, depression score from HADS, age-11 IQ and SES: Cortical thickness= b 0 Intercept+ b 1 Gender+ b 2 Exact_Age_At_Scanning+ b 3 PackYears + b 4 HDL_Cholesterol+ b 5 LDL_Cholesterol+ b 6 HDL_Cholesterol_Ratio+ b 7 Triglycerides+ b 8 Diastolic_Pressure+ b 9 Systolic_Pressure+ b 10 HighBloodPressureHistory + b 11 Stroke_History+ b 12 Fazekas_Score + b 13 Cardiovascular_Disease_History + b 14 FEV1+ b 15 Weekly_Alcohol_Units+ b 16 Hemoglobin_A1C+ b 17 Diabetes_Diagnosis + b 18 HADS+ b 19 Age-11_IQ+ b 20 SES+error To assess whether the association between smoking and cortical thickness varied as a function of the age of starting smoking, Models 2 and 3 were retested after including smoking starting age' and the smoking starting age' by pack-years' interaction term

PMID: 35138954 pubmed.ncbi.nlm.nih.gov/35138954/
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None of the three were regular users, but they had consumed cannabis before
How much you should use varies based on need and equipment