I'm doing research comparing a specific type of law, for example regarding marijuana possession, across states. What is the best way to search state law? Do I need to go state-by-state to find a state-specific database, or is there a better way? I'm finding this not to be straightforward at all - very unlike searching federal law and legislation.
It is inherently and intrinsically harder to search the laws of 50 states and compare them than it is to review a single body of federal law.
Also, case law and statute law, are researched quite differently, even though they can cover the same topics. Word searches work well for some kinds of case law issues, but poorly for statutes and regulations. Some issues, however, are hard to research with word searches, even if they involve case law.
Westlaw codes the important legal holdings of every published case in categories based upon their "key" system which has a subject-matter based digest of all case law. If you find one case with a key code that is on point, you can search all 50 states for that.
The "Restatements of Law" (e.g. Restatement of Contracts, Restatement of Torts) purports to be a summary of the majority common law rules in the named subject area, although it often reflects the lead author and supporting drafting committee's view on the "better rule" rather than the majority rule. These are very influential and often cited by courts in states where there is no case law on point. Some have been updated several times to reflect changes in the common law over time in different subject areas (e.g. the original Restatement of Contracts favored form over substances in a way that the later version do not). The American Bar Association signs off on these before they are published.
The National Conference of State Legislatures promulgates "Uniform" and "Model" acts that states may adopt with or without amendment and tracks which states have adopted them and with what modifications.
Most areas of law are the subject of legal treatises that make comprehensive 50 state summaries of relevant case law, one or two of which are typically the "leading treaties" and widely used and relied upon.
Many law review articles will do summaries of as many states' laws as possible on a given issue.
Many lobbying and special interest groups and also nolo.com prepare 50 state summaries. A good, reasonably up to date and accurate source on many topics is Wikipedia.
Ultimately, all secondary sources rely on somebody digging through state statutes in every state, analyzing them and coding them accurately, usually with citations to the source material. In fast changing areas of law this can be tricky, since laws of the same subject could be codified in different kinds of places (e.g. one might put something in a criminal code, while another might put it in a public health code or a regulation rather than a statute).
Every legal search engine (there are about half a dozen main ones, one or two of which are free) allows for 50 state searches in some form of primary legal materials like statutes and published appellate cases.