Alleged Drug Usage by a Parent-- It's not that easy to get testing ordered.........
The best way to know if you or the other parent could be affected negatively, is to assume you WOULD be affected and then go from there.
The family court must make a finding and there must be evidence that there is habitual, frequent or continual illegal use of alcohol or drugs by the parent for it to have the power to make a court order for testing.
- In other words, if you cannot prove ahead of time by corroborating evidence of the habitual, frequent or continual illegal use, and only can show possession---that won't get it.
There is no bright line law or family case law currently in California which seals a parent's fate as to
"marijuana" in general
right now, and there is not likely a published case on using non appropriate media as a sole reason for denial of custody (although we have had cases where porn movies being shown and allegations of abuse have resulted in loss of visitation...)
There is a non certified
dependency case involving some marijuana issues (not a family law case; it is an unpublished Los Angeles appeal under Juvenile Court Law, DCSS and involved two teenage kids, 15/14 at the time...).
Custody is likely to be highly affected by Domestic violence TROs, inappropriate punishment, inappropriate drug use, abusive situations, neglect, etc. Parents with DV charges or TROs against them cannot usually be the custodial parent. We see some parents accept DV TRO charges for one reason or another, but generally, it's best to fight such charges in most cases. We also see many females use DV TROs when they have no grounds. Occasionally males may do the same.
Although attorney herein has research knowledge on medicinal marijuana and various state law issues involving same, there is no one criteria in either medicinal marijuana or recreational marijuana, that would be the 100% certain win or lose factor for a parent, because in most cases, it's only one issue, and not the ONLY issue at hand. Depending on how many other issues are involved, the credibility of each parent, the depth of insight that the attorney has, and how well an attorney can size up each parent, this can make or break a case.
Simply hiring "experts" means who can afford more--it doesn't mean necessarily that one parent really wins. It will also depend on how well each parent can present him or herself, answer questions, and understand how the mediation process works. Attorney of this website has seen countless cases involving mediation, and has seen some cases go sideways at mediation, because the client may ruin his or her case by saying the wrong things.Attorneys are not allowed in mediation, therefore attorney can only try to teach client how mediators operate so they will understand what is actually being done. Attorney has seen extremely biased mediators (judging from the report they put out) over the years, good mediators, and those that are fair. Underestimating the mediation process usually results in bad results.
Attorney herein researches these issues as they apply to California Family Law, and makes best efforts to remain current on new cases or decisions. Attorney is well aware of the long running case involving marijuana, from Butte County that then seeming moved to another county just north of Butte, with varying detriment (depending on what one considers detrimental...)
In any event, any type of drug, even if it's a prescription, can be cause for concern in a divorce case. 
We all know that alcohol use can be a concern, but it's legal to buy it, right, and even to consume in the home? We have seen many court orders where alcohol is NOT to be consumed during one parent's custody.
And it's legal to obtain many drugs straight off the shelf at the store.
When courts have to consider whether drug usage is going to affect custody, it will depend on what evidence is available, how good the attorney is at setting up the defense or attack of the issue, what the exact facts are and are they verifiable, and how; essentially, all of the foundation requirements for evidentiary hearing, and all of the foundation requirements for supporting evidence should be known; further, the lack of such evidence and the preclusion possibilities, as with all evidence, will come into play.
Trying cases with drugs involved should be left to attorneys who handle trials, because the proof and litigation aspects can be done with more precision. Many clients don't want to spend the funds to engage litigators to gain appropriate custody because they do not understand the time involved to make the defense, or the admissibility for proper charging evidence.
In family law we usually see many clients that just believe all they have to do is say something, and that makes it true. That is not the case necessarily. Conversely, clients often believe they can just say something is not true, and that will prove their case. That too is not necessarily true, because if it was, then there would be no NEED for any attorneys at all, because clients could prove everything themselves?
Obviously, clients, at least most of them, are not able to do that because they did not go to law school and then work for 20+ years at honing their skill.
We have to deal with inaccurate facts, misleading statements, the social media nightmare, Facebook (often the absolute worst), and tons of Internet postings, admissions, accusations, texts, blogging, examples:
Lively, Instagram, Vine, Snapchat, Kiks Messenger, WhatsApp, GroupMe,tumblr, Twitter,Musical.ly, You Now: Broadcast,Chat,and Watch Live Video, Burn Note,Whisper, Yik Yak; could be inappropriate.........
--- Omegle+Tinder ( not appropriate for kids). Some of these apps will or can be hidden or disappear, or may cause kids to meet up with others that could be predators-- with parents not even knowing it is happening.
New apps come out all the time and they will never stop. These things can be worse than drugs in some ways as unknown people can take advantage of kids, teens, etc. A parent would never even know because most parents don't really know what kids are doing with their phones.
Personally, we would not give kids a phone, computer or any electronic device which was NOT monitored, it is very easy to obtain software to do this!
