There is some evidence that there might be a genetic component to some drug misuse disorders. Specifically, I know that there's been some research done with nicotine here (either out of Columbia or Radboud, don't really remember). Most researchers are still of the opinion that environmental factors have much more effect on drug misuse disorders than genetic.

The trope of "your first dose will get you hooked" is patently false. There's no evidence that this is true. Anecdotal anything, especially with drugs, doesn't mean anything, and all of these outlier anecdotes are actively damaging to the education of the public with regards to drugs.

Google these genetic polymorphisms + alcoholism that I copy and pasted below, there is your proof :)

Genetic polymorphisms that may increase risk of alcohol abuse Wild type ADH1B1 allele and wild type ALDH21 may increase the risk of alcohol use disorder because no acetaldehyde build up is associated with normally-functioning ADH and ALDH enzymes. Several studies have shown association of ADH1B1 and ALDH21 with alcoholism, especially in the Asian population. Kim et al. studied 1032 Korean subjects and concluded alcohol dependence in 86.5% alcoholic subjects could be attributed to ADH1B1 and or ALDH21 [14]. Tolstrup et al., in a large study involving genotyping of 9080 white men and women from the general population and using the brief Michigan Alcoholism Screening test, concluded that men with ADH1B1/1 genotype (wild type homozygous) had a two to fourfold higher risk of developing alcoholism compared to men with ADH1B2/1 or ADH1B2/2 genotype. The authors further commented that because ADH1B1 allele is found in more than 90% Caucasians and less than 10% East Asians, the population attributable risk of alcoholism by ADHB1/*1 homozygous genotype was 62% among Caucasians compared with 24% among the East Asian population [15].

Google these genetic polymorphisms + alcoholism that I copy and pasted below, there is your proof :)

Genetic polymorphisms that may increase risk of alcohol abuse Wild type ADH1B1 allele and wild type ALDH21 may increase the risk of alcohol use disorder because no acetaldehyde build up is associated with normally-functioning ADH and ALDH enzymes. Several studies have shown association of ADH1B1 and ALDH21 with alcoholism, especially in the Asian population. Kim et al. studied 1032 Korean subjects and concluded alcohol dependence in 86.5% alcoholic subjects could be attributed to ADH1B1 and or ALDH21 [14]. Tolstrup et al., in a large study involving genotyping of 9080 white men and women from the general population and using the brief Michigan Alcoholism Screening test, concluded that men with ADH1B1/1 genotype (wild type homozygous) had a two to fourfold higher risk of developing alcoholism compared to men with ADH1B2/1 or ADH1B2/2 genotype. The authors further commented that because ADH1B1 allele is found in more than 90% Caucasians and less than 10% East Asians, the population attributable risk of alcoholism by ADHB1/*1 homozygous genotype was 62% among Caucasians compared with 24% among the East Asian population [15].

Thanks for that. However, those studies only show that a certain gene is more prevalent in alcoholics, not that people with that gene "do not have the same liberty with regard to alcohol as others do" nor that "their agency is impaired when confronted with decisions about alcohol".

Also, I still don't see any studies showing this for any of the other drugs that have actually been made illegal, which would be more to the point.