Abstract: Approximately 7-14.4% of children with Attention deficit hyperactivity disorer ADHD have a co-morbid tic disorder (Tourette disorer TD). The co-morbidity of the two disorders leads to confusion in clinical diagnosis, contradictory medication, and limited efficacy. The child’s behavioral problems are more prominent and social adjustment is lower. It is a clinical problem that cannot be ignored. This article provides an overview and discussion of the diagnosis and pharmacological treatment of co-morbidities. The Spencer study showed that 7% of children with ADHD have a combination of Tourette disorer TD. The co-morbidity rate of ADHD and TD reported in China is 14.4%, and the existence of ADHD co-morbidity may lead to confusion in clinical diagnosis, contradictory medication, limited efficacy, more prominent behavioral problems, and poor social adjustment. It is a clinical problem that cannot be ignored. This paper provides an overview and discussion of the diagnosis and pharmacological treatment of ADHD combined with TD. 1. Diagnosis of attention deficit hyperactivity disorder combined with tic disorder Based on the clinical information collected from diagnostic interviews with children, parents and teachers, the diagnosis of the two disorders can be made if the clinical information meets the criteria of DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th edition) or ICD-10 (International Classification of Diseases, 10th edition) regarding the typology and classification of ADHD and TD. Since overlapping symptoms of behavioral disorders are more common, and children with ADHD with TD usually have ADHD symptoms before TD symptoms. Therefore, the onset of TD symptoms is usually later than the onset of ADHD symptoms in terms of the onset of the disease. In this way, inattention and hyperactivity secondary to tic disorder can also be excluded. In a small number of children, ADHD and TD symptoms may also occur together. Many scholars regard it as a subtype of ADHD rather than as a co-morbidity of the two disorders. Some children with ADHD may develop tics when treated with central stimulants. However, most of these are transient. The tic symptoms did not worsen with continued medication. This is simply a side effect of central stimulant treatment for ADHD. It should be distinguished from ADHD and TD co-morbidities. 2. Medication for attention-deficit hyperactivity disorder combined with tic disorder 2.1. The efficacy of central stimulants such as Ritalin and amphetamines in the treatment of ADHD is definite. About 75% to 90% of children with ADHD improve their symptoms after taking the drugs. They are used to increase the concentration of neurotransmitters such as dopamine and norepinephrine in the synaptic gap of neurons by binding and blocking dopamine transporters, promoting dopamine release, inhibiting its reuptake, and inhibiting the activity of monoamine oxidase, thus playing a therapeutic role. However, due to the increased central excitability, about 15-30% of children with ADHD develop twitching symptoms during treatment. Thus, there is a risk of exacerbating or inducing tic disorders when central stimulants are administered to treat ADHD. On the contrary, if children with ADHD and TD are given dopamine receptor blockers such as haloperidol and Tebutramine to control their tic symptoms while being treated with central stimulants, the therapeutic effect of central stimulants on ADHD may also be affected. 2.2. Choice of therapeutic drugs ADHD predisposes children to learning difficulties and a wide range of behavioral problems. The co-existing tic disorder has little effect on the psychosocial functioning of the child. Therefore, ADHD symptoms are often more damaging than TD symptoms. The author suggests that the following principles should be followed in the selection of therapeutic drugs. 2.2.1 The type of ADHD with TD is milder transient tics. Central stimulants are preferred for the treatment. The main focus is to control the symptoms of ADHD. The literature reports that ADHD with twitching is safe to be treated with central stimulants. Tic symptoms in susceptible individuals may be induced or exacerbated only with chronic or high doses of central stimulants in children with ADHD. Most of these effects are reversible. TD symptoms are mostly reduced or exacerbated with psycho-behavioral treatment. Most of the twitching symptoms can be reduced or not aggravated. 2.2.2 For ADHD with severe tic disorders, such as severe transient tics, Tourette*s syndrome, etc., the choice of medication needs to be balanced between the two. For these children, a combination of small doses of central stimulants (such as Ritalin) and conventional doses of dopamine receptor blockers (such as Tebrile) can be used first. The author has used a combination of low-dose Ritalin during the school day and haloperidol after school to divert the maximum concentration of these two drugs in the body to minimize the “antagonistic effect” of their combined use. Both ADHD and TD symptoms were somewhat controlled. The next option is to use a drug that is effective in both ADHD and TD, such as Clomidine. This drug is an а2 agonist and was originally used clinically as an antihypertensive drug. In the late 1980s, it was found to have a therapeutic effect on tic disorders. Recently, it has been found to be effective in ADHD as well. The mechanism of action is not yet precise. The drug can increase brain arousal, reduce hyperactivity and improve impulsive behavior. However, it is not as effective as Ritalin in enhancing attention. A controlled clinical study of the two co-morbidities showed that the combination of Ritalin and colistin was more effective than colistin treatment alone. However, side effects such as colistin drowsiness, excessive sedation, dry mouth, headache, nausea, and abdominal pain are more common. Side effects such as dizziness, ataxia, slowed heart rate and hypotension at higher doses also limit its application. In contrast, guanfacine, a new type of а2 agonist, is effective in the treatment of ADHD and TD. It is especially suitable for older children and adult patients. The cardiovascular side effects are less than those of colistin. The combination of antidepressants promethazine and haloperidol can also be used in patients with ADHD with TD who have symptoms of depression and anxiety. Because of the significant cardiovascular side effects of promethazine, the effects of long-term treatment can be significantly reduced. Therefore, they should be used with caution or sparingly in childhood. 2.2.3 The progress of drugs for the treatment of co-morbidities In recent years, Lofexidine and Pergolide have been reported as drugs for the treatment of co-morbidities. Niederhofer et al. reported that 44 children with mixed ADHD and TD (41 males and 3 females, mean age 10.4 years) were treated with lofexidine and placebo in a randomized, double-blind trial for 8 weeks. was superior to the placebo group. One case in the lofexidine treatment group was discontinued due to the sedative effect of the drug. The side effects of lofexidine in terms of hypotension and heart rate slowing did not affect the continuation of treatment. The dopamine agonist pergolide was originally used as an adjunct to levodopa in the treatment of Parkinson’s disease, as reported by Gilbert et al. A randomized, double-blind controlled trial of pergolide in 57 children aged 7 to 17 years with tic disorder showed that it was safe and effective in the treatment of tic disorders and also improved symptoms of attention deficit hyperactivity disorder. There is no report on the use of these drugs in children for the treatment of co-morbidities in China. 2.3 Points to note when using Ritalin in co-morbidities In view of the aforementioned contradictory nature of drug treatment for ADHD and TD, the following points should be noted when giving Ritalin, a central nervous stimulant, to co-morbidities, either alone or in combination with anti-twitch disorder drugs. 2.3.1. Ritalin should be used in small doses because too high a dose may aggravate tic symptoms while controlling ADHD symptoms. Therefore, we should start with a small dose and gradually increase to the “optimal dose”. The so-called “optimal dose” refers to the ability to achieve maximum control of ADHD symptoms while minimizing the impact on tic symptoms. Generally, it is safe to use no more than 0.3mg/Kg of Ritalin daily. 2.3.2 Long-acting central stimulants are not suitable for patients with both diseases. Long-acting central stimulants such as Ritalin controlled-release tablets (Concerta), norepinephrine reuptake inhibitors (Atomonetine) and Pemoline (Pemoline) have a long half-life in the body and maintain the effect for up to 12 hours. It is easy to control the symptoms of ADHD while aggravating the symptoms of twitching, which makes it difficult for the child to adhere to treatment. 2.3.3. Make regular follow-ups The duration of medication, dose and side effects should be recorded in detail during treatment. As Ritalin short-acting preparations once oral its maintenance effect time is only 3 to 4 hours, the effect of the drug are children in school time. Therefore, the teacher’s feedback on the changes in the child’s symptoms before and after taking the medication is often more in line with the actual situation than the parents’ complaints. Based on the information obtained through communication with the child, parents and teachers and the results of the Conners scale, a comprehensive analysis is needed to assess whether the dose of Ritalin should be adjusted.